When social psychologist Brad Bushman handed out voodoo dolls to 107 married couples, he knew those dolls were in for a lot of stabbing.

Each married person who volunteered for his study got a doll and 51 pins. Bushman and his fellow psychologists instructed the volunteers to stab a doll, representing their spouse, each night with more pins depending how angry they were with their spouse. When people had low blood sugar around stabbing time, they went through a lot of pins.